Centaurus A

Centaurus A
ESA/Herschel/PACS/SPIRE/VNGS ;
ESA/XMM-Newton/EPIC

Small, Unannotated - Small, Annotated
Large, Unannotated - Large, Annotated

Observations by the two of the European Space Agency's space observatories have provided a multi-wavelength view of the mysterious galaxy Centaurus A. The new images, from the Herschel Space Observatory and the XMM-Newton x-ray satellite, are revealing further hints about its cannibalistic past and energetic processes going on in its core.

At a distance of around 12 million light years, Centaurus A is the closest large elliptical galaxy to our own Milky Way. It has been marked as unusual since shortly after its discovery in the 19th century due to a thick lane of dust across its centre – an unusual feature for an elliptical galaxy. But it wasn't until a century later that the galaxy’s true nature was revealed.

Emanating from its core are two massive jets of material streaming from a massive black hole in the heart of Centaurus A. When observed by radio telescopes, the jets stretch for up to a million light years, though the Herschel and XMM-Newton results focus on the inner regions.

“Centaurus A is the closest example of a galaxy to us with massive jets from its central black hole,” explained Prof Christine Wilson of McMaster University, Canada, who is leading the study of Centaurus A with Herschel. “Observations with Herschel, XMM-Newton and telescopes at many other wavelengths allow us to study their effects on the galaxy and its surroundings.”

Centaurus A in visible light, showing the dark dust lane across its centre
Image credit: ESO.

Centaurus A as seen in far-infrared light by Herschel, showing the twisted disc in the centre, the jets from the black hole, and two clumps of dust. Image credit: ESA/Herschel/SPIRE/PACS

Strong radio emission is caused by electrons travelling at close to the speed of light through strong magnetic fields, and is so bright that the jets are even visible in the far-infrared images from the Herschel Space Observatory. As well as the jets, the images from this infrared observatory also show a twisted disc of dust near the galaxy’s centre.

This odd shape is strong evidence that Centaurus A underwent a cosmic collision with another galaxy in the distant past. The colliding galaxy was ripped apart to form the warped disc, and the formation of young stars heats the dust to cause the infrared glow seen by Herschel.

Such collisions often result in shells and rings of gas and dust, and Centaurus A is no exception. Herschel observations have now confirmed the presence of two clumps of dust that seem to be lined up with the two lobes of the jets.

“The apparent alignment of two clumps with the two jets now seems to be a cosmic coincidence, and it appears that the dust originated from one of the colliding galaxies.” explained Dr Robbie Auld, of Cardiff University. “Unlike most dust Herschel sees, which is heated by nearby star formation, the dust in these clumps is being heated by old stars in Centaurus A itself, up to 50,000 light years away.”

Centaurus A as seen in x-rays by XMM-Newton, showing the jets from the black hole and the super-heated gas. Image credit: ESA/XMM-Newton/EPIC

In x-rays the effect of the two jets of material is clearly visible. Showing the presence of extremely hot gas, the images from the XMM-Newton x-ray satellite clearly show the axis of the one of the jets. While the other jet itself is not seen in by XMM-Newton, the gas it is ploughing into is shocked and heated to very high temperatures, creating a bright x-ray glow.

“XMM-Newton is the observatory most suited to detecting extended weak X-ray emission, often allowing us to see halos around galaxies for the first time,” notes Norbert Schartel, XMM-Newton Project Scientist.

In the centre of the galaxy, the massive black hole is also having an effect on its immediate surroundings. The material around it glows brightly in x-rays, but there Herschel has identified an apparent deficit of dust within a few thousand light years of the black hole.

“This could be due to intense x-rays destroying the tiny dust grains, or due to the way the warped ring of dust is affecting star formation” said Prof Wilson. “Either way, Centaurus A is the ideal place to study the extreme processes that occur near super-massive black holes"

Centaurus A at visible, far-infrared and x-ray wavelengths. Image credit:ESA/Herschel/SPIRE/PACS/VNGS (far-infrared) ; ESA/XMM-Newton/EPIC (x-ray) ; ESO (visible). Click view

More about → Centaurus A

Herschel Helps Solve Mystery of Cosmic Dust Origins

This layout compares two pictures of a supernova remnant called SN 1987A -- the left image was taken by the Herschel Space Observatory, and the right is an enlarged view of the circled region at left, taken with NASA's Hubble Space Telescope. Image credit: ESA/NASA-JPL/UCL/STScI. Full image and caption

This plot shows energy emitted from a supernova remnant called SN 1987A. Previously, NASA's Spitzer Space Telescope detected warm dust around the object. Image credit: ESA/NASA-JPL/UCL/STScI . Full image and caption

PASADENA, CALIF. -- New observations from the infrared Herschel Space Observatory reveal that an exploding star expelled the equivalent of between 160,000 and 230,000 Earth masses of fresh dust. This enormous quantity suggests that exploding stars, called supernovae, are the answer to the long-standing puzzle of what supplied our early universe with dust.

"This discovery illustrates the power of tackling a problem in astronomy with different wavelengths of light," said Paul Goldsmith, the NASA Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who is not a part of the current study. "Herschel's eye for longer-wavelength infrared light has given us new tools for addressing a profound cosmic mystery."

Herschel is led by the European Space Agency with important contributions from NASA.

Cosmic dust is made of various elements, such as carbon, oxygen, iron and other atoms heavier than hydrogen and helium. It is the stuff of which planets and people are made, and it is essential for star formation. Stars like our sun churn out flecks of dust as they age, spawning new generations of stars and their orbiting planets.

Astronomers have for decades wondered how dust was made in our early universe. Back then, sun-like stars had not been around long enough to produce the enormous amounts of dust observed in distant, early galaxies. Supernovae, on the other hand, are the explosions of massive stars that do not live long.

The new Herschel observations are the best evidence yet that supernovae are, in fact, the dust-making machines of the early cosmos.

"The Earth on which we stand is made almost entirely of material created inside a star," explained the principal investigator of the survey project, Margaret Meixner of the Space Telescope Science Institute, Baltimore, Md. "Now we have a direct measurement of how supernovae enrich space with the elements that condense into the dust that is needed for stars, planets and life."

The study, appearing in the July 8 issue of the journal Science, focused on the remains of the most recent supernova to be witnessed with the naked eye from Earth. Called SN 1987A, this remnant is the result of a stellar blast that occurred 170,000 light-years away and was seen on Earth in 1987. As the star blew up, it brightened in the night sky and then slowly faded over the following months. Because astronomers are able to witness the phases of this star's death over time, SN 1987A is one of the most extensively studied objects in the sky.

A new view from NASA's Hubble Space Telescope showing how supernova 1987A has recently brightened is at http://hubblesite.org/newscenter/archive/releases/2011/21 .

Initially, astronomers weren't sure if the Herschel telescope could even see this supernova remnant. Herschel detects the longest infrared wavelengths, which means it can see very cold objects that emit very little heat, such as dust. But it so happened that SN 1987A was imaged during a Herschel survey of the object's host galaxy -- a small neighboring galaxy called the Large Magellanic Cloud (it's called large because it's bigger than its sister galaxy, the Small Magellanic Cloud).

After the scientists retrieved the images from space, they were surprised to see that SN 1987A was aglow with light. Careful calculations revealed that the glow was coming from enormous clouds of dust -- consisting of 10,000 times more material than previous estimates. The dust is minus 429 to minus 416 degrees Fahrenheit (about minus 221 to 213 Celsius) -- colder than Pluto, which is about minus 400 degrees Fahrenheit (204 degrees Celsius).

"Our Herschel discovery of dust in SN 1987A can make a significant understanding in the dust in the Large Magellanic Cloud," said Mikako Matsuura of University College London, England, the lead author of the Science paper. "In addition to the puzzle of how dust is made in the early universe, these results give us new clues to mysteries about how the Large Magellanic Cloud and even our own Milky Way became so dusty."

Previous studies had turned up some evidence that supernovae are capable of producing dust. For example, NASA's Spitzer Space Telescope, which detects shorter infrared wavelengths than Herschel, found 10,000 Earth-masses worth of fresh dust around the supernova remnant called Cassiopea A. Hershel can see even colder material, and thus the coldest reservoirs of dust. "The discovery of up to 230,000 Earths worth of dust around SN 1987A is the best evidence yet that these monstrous blasts are indeed mighty dust makers," said Eli Dwek, a co-author at NASA Goddard Space Flight Center in Greenbelt, Md.

Other authors include M. Otsuka, J. Roman-Duval, K.S. Long and K.D. Gordon, Space Telescope Science Institute, Baltimore, Md.; B. Babler, University of Wisconsin, Madison; M.J. Barlow, University College London, United Kingdom; C. Engelbracht, K.A. Misselt and E. Montiel, University of Arizona, Tucson; K. Sandstrom, Max Planck Institut für Astronomie, Heidelberg, Germany; M. Lakicevic and J.Th. van Loon, Keele University, United Kingdom; G. Sonneborn, Goddard Space Flight Center, Greenbelt, Md.; G.C. Clayton, Louisiana State University, Baton Rouge; P. Lundqvist, Stockholm, Sweden; T. Nozawa, University of Tokyo, Japan; S. Hony, K. Okumura and M. Sauvage, the French Alternative Energies and Atomic Energy Commission, France.

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information is online at http://www.nasa.gov/herschel and http://www.esa.int/SPECIALS/Herschel/index.html .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

More about → Herschel Helps Solve Mystery of Cosmic Dust Origins